Submersible pumps find many uses wherein liquid or slurry containing solid matter needs transporting, such as in mining, at building sites, in the treatment of waste or sewage, in flooded land areas, etc. A typical submersible pump that is used in these applications is the centrifugal pump wherein liquid transport is generated by an impeller pump wheel in rotation, sucking liquid and any solid matter entrained therein through an axial inlet on the suction side of the pump, and accelerating the liquid and solid matter through centrifugal action via a radial discharge on the pressure side of the pump. The literature contains numerous embodiments of the centrifugal pump which is well known to the public.
The literature also contains several examples of pump solutions by which solid matter entrained in liquid is cut down to fractions, the size of which this way is adapted to pass through the pump without obstructing its operation. Obviously this method applies only to solid matter that is possible to cut in a shearing action, generated typically by means of elements in relative rotation as the pump is operating.
Submersible pumps are however also applied in connection with liquids and slurry containing hard solid matter that is not suitable for cutting, such as minerals, metal, hard wood and synthetics. In applications where hard solid matter is not screened or otherwise extracted from the liquid, the pump needs to be structured to admit the solids to pass through the pump. Any measure to this purpose which includes the provision of permanent gaps between rotary and stationary components of the pump will hamper the pump's capacity, and will not completely avoid the risk of extraordinary sized solids getting wedged between the components in relative rotation.
WO 2007/004943 A1 suggests another approach to this problem. A submersible centrifugal pump is disclosed and structured to effect ejection of solids that would potentially obstruct the operation of the pump. An impeller is keyed to the end of a drive shaft through a coupling that permits the impeller to be displaced axially relative to an impeller seat at the pump intake. A solid of a size that may not be propelled through the pump in normal operation will cause the impeller to lift from the impeller seat, forming a gap there between through which the solid is ejected into the discharge flow. The impeller is then caused by the pressure difference over the impeller to return to its normal operation in close rotation to the impeller seat.
Although the operation is satisfactory as expected, improvements of the ejector function are still possible.